(a) Technical Field
The present invention relates to a lithium ion-conductive sulfide-based solid electrolyte which may include nickel sulfide and, accordingly, provide a novel structure and performance of an all-solid state battery.
(b) Background Art
Secondary batteries have been broadly used in small devices, such as mobile phones, camcorders, and notebooks, as well as large devices, such as vehicles and power storage systems. Accordingly, requirements for safety and high performance of batteries have been increased as secondary batteries can be applied to a variety of areas.
A lithium secondary battery, one type of secondary battery, has advantages such as high energy density and capacity per unit area, compared to a nickel-manganese battery or a nickel-cadmium battery.
However, in conventional lithium secondary batteries, a liquid electrolyte such as an organic solvent has been mostly used. Accordingly, problems related to safety, such as a risk of fire due to leakage of an electrolyte may be continuously raised.
Recently, in order to enhance safety, attention to an all-solid state battery using an inorganic solid electrolyte, instead of an organic liquid electrolyte, as an electrolyte has been increased. For example, a solid electrolyte has incombustibility or flame retardancy, and thus, may be safer than the liquid electrolyte.
A solid electrolyte may include an oxide-based solid electrolyte and a sulfide-based solid electrolyte. The sulfide-based solid electrolyte has high lithium ion conductivity, compared to the oxide-based solid electrolyte. In addition, the sulfide-based solid electrolyte has high process flexibility due to superior ductility, thereby being variously utilized.
For example, compounds such as Li3PS4 and Li7P3S11 have been mainly used as sulfide-based solid electrolytes. However, these compounds may have less lithium ion conductivity, compared the liquid electrolyte.
In the related arts, U.S. Patent No. 2014-0193693 has disclosed that elements such as aluminum (Al), silicon (Si), iron (Fe), nickel (Ni), and zirconium (Zr) can be added to a sulfide-based solid electrolyte such as thio-LISICON in order to increase lithium ion conductivity. However, in the sulfide-based solid electrolyte, ranges of composition ratios of sulfur (S), lithium (Li), and phosphorus (P) exhibiting high lithium ion conductivity may be limited. In addition, t lithium ion conductivity may increases when the elements are added, however, and have not suggested quantitative correlations, and the like among the elements, sulfur (S), lithium (Li), and phosphorus (P).
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.